Yu-Hua Wen

Could Borophene Be Used as a Promising Anode Material for High-Performance Lithium Ion Battery?

The rapid development of electronic products has inspired scientists to design and explore novel electrode materials with an ultrahigh rate of charging/discharging capability, such as two-dimensional (2-D) nanostructures of graphene and MoS2. In this study, another 2-D nanosheet, that is a borophene layer, has been predicted to be utilized as a promising anode material for high-performance Li ion battery based on density functional theory calculations. Our study has revealed that Li atom can combine strongly with borophene surface strongly and easily, and exist as a pure Li(+) state. A rather small energy barrier (0.007 eV) of Li diffusion leads to an ultrahigh diffusivity along an uncorrugated direction of borophene, which is estimated to be 10(4) (10(5)) times faster than that on MoS2 (graphene) at room temperature. A high Li storage capacity of 1239 mA·h/g can be achieved when Li content reaches 0.5. A low average operating voltage of 0.466 V and metallic properties result in that the borophene can be used as a possible anode material. Moreover, the properties of Li adsorption and diffusion on the borophene affected by Ag (111) substrate have been studied. It has been found that the influence of Ag (111) substrate is very weak. Li atom can still bind on the borophene with a strong binding energy of -2.648 eV. A small energy barrier of 0.033 eV can be retained for Li diffusion along the uncorrugated direction, which can give rise to a high Li diffusivity. Besides, the performances of borophene-based Na ion battery have been explored. Our results suggest that an extremely high rate capability could be expected in borophene-based Li ion battery.

Structure and stability of platinum nanocrystals: from low-index to high-index facets

High index surfaces are introduced into Pt nanocrystals because they are expected to exhibit higher catalytic activity than low index planes such as {111}, {100}, and even {110}. This article presents a systematic investigation on the structure and stability of polyhedral Pt nanocrystals with both low-index and high-index facets by means of atomistic simulations. It has been found that the stability of Pt nanocrystals depends strongly on the particle shape and surface structures. Those nanocrystals, enclosed by high-index facets of {310}, {311}, and {331}, possess better stability and higher dangling bond density of surface compared with those ones with low-index facets, such as {100} and {110}, suggesting that they should become preferential candidates for nanocatalysts. The octahedral nanocrystals with {111} facets, though they have excellent structural and thermal stabilities, present the lowest dangling bond density of surface.

Direct to indirect band gap transition in ultrathin ZnO nanowires under uniaxial compression

National Natural Science Foundation of China [10702056, 10774124]; Program for New Century Excellent Talents in Fujian Province University, China

Electrochemical Synthesis of Tetrahexahedral Rhodium Nanocrystals with Extraordinarily High Surface Energy and High Electrocatalytic Activity

Noble metal nanocrystals (NCs) enclosed with high-index facets hold a high catalytic activity thanks to the high density of low-coordinated step atoms that they exposed on their surface. Shape-control synthesis of the metal NCs with high-index facets presents a big challenge owing to the high surface energy of the NCs, and the shape control for metal Rh is even more difficult because of its extraordinarily high surface energy in comparison with Pt, Pd, and Au. The successful synthesis is presented of tetrahexahedral Rh NCs (THH Rh NCs) enclosed by {830} high-index facets through the dynamic oxygen adsorption/desorption mediated by square-wave potential. The results demonstrate that the THH Rh NCs exhibit greatly enhanced catalytic activity over commercial Rh black catalyst for the electrooxidation of ethanol and CO.

Diverse melting modes and structural collapse of hollow bimetallic core-shell nanoparticles: a perspective from molecular dynamics simulations.

Introducing hollow structures into metallic nanoparticles has become a promising route to improve their catalytic performances. A fundamental understanding of thermal stability of these novel nanostructures is of significance for their syntheses and applications. In this article, molecular dynamics simulations have been employed to offer insights into the thermodynamic evolution of hollow bimetallic core-shell nanoparticles. Our investigation reveals that for hollow Pt-core/Au-shell nanoparticle, premelting originates at the exterior surface, and a typical two-stage melting behavior is exhibited, similar to the solid ones. However, since the interior surface provides facilitation for the premelting initiating at the core, the two-stage melting is also observed in hollow Au-core/Pt-shell nanoparticle, remarkably different from the solid one. Furthermore, the collapse of hollow structure is accompanied with the overall melting of the hollow Pt-core/Au-shell nanoparticle while it occurs prior to that of the hollow Au-core/Pt-shell nanoparticle and leads to the formation of a liquid-core/solid-shell structure, although both of them finally transform into a mixing alloy with Au-dominated surface. Additionally, the existence of stacking faults in the hollow Pt-core/Au-shell nanoparticle distinctly lowers its melting point. This study could be of great importance to the design and development of novel nanocatalysts with both high activity and excellent stability.

Enhanced thermal stability of Au@Pt nanoparticles by tuning shell thickness: Insights from atomistic simulations

Development of core–shell bimetallic nanoparticles with bifunctional catalytic activity and excellent stability is a challenging issue in nanocatalyst synthesis. Here we present a detailed study of thermal stabilities of Au-core/Pt-shell nanoparticles with different core sizes and shell thicknesses. Molecular dynamics simulations are used to provide insights into the melting and diffusive behavior at atomic-level. It is found that the thermal stabilities of core-shell nanoparticles are significantly enhanced with increasing thickness of Pt shell. Meanwhile, the melting mechanism is strongly dependent on the shell thickness. When the core size or shell thickness is very small, the melting is initiated in the shell and gradually spreads into the core, similar to that of monometallic nanoparticles. As the core increases up to moderate size, an inhomogeneous melting has been observed. Due to the relatively weak confinement of thin shell, local lattice instability preferentially takes place in the core, leading to the inhomogeneous premelting of Au core ahead of the overall melting of Pt shell. The diffusion coefficients of both Au and Pt are decreased with the increasing thickness of shell, and the difference in their diffusions favors the formation of inhomogeneous atomic distributions of Au and Pt. The study is of considerable importance for improving the stability of Pt-based nanocatalysts by tuning the shell thickness and core size.

Surface-passivation-induced metallic and magnetic properties of ZnO graphitic sheet

First-principles calculations were used to investigate the electronic and magnetic properties of surface-passivated ZnO graphitic sheets. The results show that ZnO graphitic sheet with hydrogenation on both O and Zn atoms exhibits indirect band gap, while ZnO graphitic sheet is found to be metallic for hydrogenation on only O atoms and magnetic semiconducting for surface passivation by H or NH2 on only Zn atoms. The relative stability of ZnO graphitic sheet passivated by H or NH2 has also been discussed.First-principles calculations were used to investigate the electronic and magnetic properties of surface-passivated ZnO graphitic sheets. The results show that ZnO graphitic sheet with hydrogenation on both O and Zn atoms exhibits indirect band gap, while ZnO graphitic sheet is found to be metallic for hydrogenation on only O atoms and magnetic semiconducting for surface passivation by H or NH2 on only Zn atoms. The relative stability of ZnO graphitic sheet passivated by H or NH2 has also been discussed.

Thermal stability of platinum nanowires: a comparison study between single-crystalline and twinned structures

Platinum is the most active and one of most commonly used catalytic metals. In this article, atomistic simulations have been employed to systematically investigate the thermal stability of platinum nanowires with single-crystalline and fivefold twinned structures. It has been revealed that the single-crystalline nanowires possess better structural stabilities than the twinned ones. Furthermore, when subjected to continuous heating, the twinned nanowires exhibit an inhomogeneous melting, essentially different from what happens in the single-crystalline ones, and hence the lower melting point. By analyses of the microstructural evolution and dynamics behavior during the heating process, the structural transition of the nanowire is discussed and the inhomogeneity in the twinned nanowire is identified to originate from the dislocation-induced destruction of twin boundaries.

Strain-tunable band gap of hydrogenated bilayer graphene

National Natural Science Foundation of China [10702056, 10774124]; Xiamen University; Academic Award for Doctoral Candidates of China

Tetrahexahedral Pt-Pd alloy nanocatalysts with high-index facets: An atomistic perspective on thermodynamic and shape stabilities

Metallic nanoparticles with high-index facets exhibit exceptional electrocatalytic activity owing to the high density of low coordination sites at the surface, thus they have attracted intense interest over the past few years. Alloying could further improve their catalytic activity by the synergy effects of high-index facets and electronic structures of components. Using atomistic simulations, we have investigated thermodynamic and shape stabilities of tetrahexahedral Pt–Pd alloy nanoparticles respectively bound by {210} and {310} facets. Energy minimization through Monte Carlo simulations has indicated that the outermost layer is predominated by Pd atoms while Pt atoms preferentially occupy the sub-outermost layer of nanoparticles. Molecular dynamics simulations of the heating process have shown that the {210} faceted nanoparticles possess better thermodynamic and shape stabilities than the {310} faceted ones. The coordination numbers of surface atoms were used to explore the potential origin of the different stabilities. Furthermore, a high Pt ratio will help enhance their stabilities. For both faceted nanoparticles, the melting has homogeneously developed from the surface into the core, and the tetrahexahedra have finally evolved into sphere-like shape prior to the overall melting. These results are helpful for understanding the composition and thermodynamic properties of high-index faceted nanoparticles, and are also of practical importance to the development of alloy nanocatalysts.